Nassau County is suing its five public employee unions, asking a judge to invalidate a September 2017 agreement made under the Mangano administration that could restore pay to longtime workers and prevent layoffs through July.

The complaints, filed in state Supreme Court on March 9, address a memorandum of agreement between former Chief Deputy County Executive Rob Walker with each of Nassau’s major unions: Civil Service Employees Association, Police Benevolent Association, Superior Officers Association, Corrections Officers Benevolent Association and Detectives Association Inc.

The lawsuits, all separate filings, mirror one another in arguing the Walker agreement is “not enforceable because it is based upon a mutual mistake of fact.”

Attorneys representing the county say the deal Walker and union leaders struck was based on the assumption that “longevity” pay for county workers would be restored at the beginning of 2018, according to court papers. But when the unions negotiated their most recent contract, the Nassau Interim Finance Authority agreed to lift the wage freeze but not the longevity pay.

The pacts are said to cost the county more than $10 million and had been called into question before — just days after being signed on Sept. 15, 2017. County Executive Laura Curran’s administration, in a recent budget memo to NIFA last week, said funds for the new collective bargaining agreement have not been factored into the budget. Before union negotiations begin, the county needs to resolve whether the Walker memorandum of agreement is legally binding, the administration wrote.

Curran spokesman Michael Martino said the administration would not comment on pending litigation.

The leader of the largest county union is reluctant to back away from the pact.

Sign up for the Power on Trial newsletter

Get our insider's look and analysis of the key moments in the Manganos' retrial.

“We feel confident that we have a valid agreement. It was signed by the chief deputy county executive and the county attorney was instrumental in amending its language,” said Jerry Laricchiuta, president of Civil Service Employees Association Local 830.

Laricchiuta acknowledged that the county attorney at the time, Carnell Foskey, questioned the deal between Walker and the unions.

Foskey, the top attorney under the Mangano administration, also said in a September letter the county-union agreements “exceed the ordinary terms and usual substance” of such deals, and would need approval from the county legislature and Nassau’s financial control board.

Longevity payments are factored into employee salaries after workers have been with the county for a certain number of years. The payments have remained the same since 2011, when NIFA imposed a wage freeze. When a 2014 contract deal lifted that freeze, longevity increases were not restored, and so many county workers are owed several thousand dollars each in retroactive longevity pay. Also part of Walker’s September 2017 pact with the unions was a promise of no layoffs through July 2018 if the unions deferred half of the longevity pay — which would save the county $5 million.

Laricchiuta said longevity pay is important to the employees he represents — the largest collective bargaining unit in the county — because they are among the lowest paid, with a median income of about $58,000. Other union leaders, Nassau County PBA president James McDermott and SOA president Kevin Black, said they would not comment on pending litigation.

Nassau employs about 7,000 full-time unionized workers. The collective bargaining agreements with each of Nassau’s five public employee unions expired on Dec. 31, 2017.

“I’m not sure this is the way to go about it,” Nassau County Legislature Presiding Officer Richard Nicolello (R-New Hyde Park) said when asked about the lawsuits. “It (longevity pay) should be a conversation at the bargaining table. That’s probably where it belongs.”

Walker, 43, a Republican and former state assemblyman from Hicksville, surrendered to federal officials in February, pleading not guilty to obstructing justice and lying to FBI agents.

The felony charges against him are the result of an ongoing federal investigation into whether Nassau public officials have taken money from county contractors and if those parties then tried to conceal their actions.

Legis. Delia DeRiggi-Whitton (D-Glen Cove) said she believed that Walker overstepped his authority in the agreement with the unions and that the lawsuits are more about “a question of procedure.”

“It’s not that we don’t want to address longevity — we all know that at some point it will be discussed — but there are real questions about whether Mr. Walker had the authority to do this. I would argue that he did not.”